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50b7b6f29d
As io_threads are fully set up USER threads it's clearer to separate the
code path from the KTHREAD logic.
The only remaining difference to user space threads is that io_threads
never return to user space again. Instead they loop within the given
worker function.
The fact that they never return to user space means they don't have an
user space thread stack. In order to indicate that to tools like gdb we
reset the stack and instruction pointers to 0.
This allows gdb attach to user space processes using io-uring, which like
means that they have io_threads, without printing worrying message like
this:
warning: Selected architecture i386:x86-64 is not compatible with reported target architecture i386
warning: Architecture rejected target-supplied description
The output will be something like this:
(gdb) info threads
Id Target Id Frame
* 1 LWP 4863 "io_uring-cp-for" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
2 LWP 4864 "iou-mgr-4863" 0x0000000000000000 in ?? ()
3 LWP 4865 "iou-wrk-4863" 0x0000000000000000 in ?? ()
(gdb) thread 3
[Switching to thread 3 (LWP 4865)]
#0 0x0000000000000000 in ?? ()
(gdb) bt
#0 0x0000000000000000 in ?? ()
Backtrace stopped: Cannot access memory at address 0x0
Fixes: 4727dc20e042 ("arch: setup PF_IO_WORKER threads like PF_KTHREAD")
Link: https://lore.kernel.org/io-uring/044d0bad-6888-a211-e1d3-159a4aeed52d@polymtl.ca/T/#m1bbf5727e3d4e839603f6ec7ed79c7eebfba6267
Signed-off-by: Stefan Metzmacher <metze@samba.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Andy Lutomirski <luto@kernel.org>
cc: linux-kernel@vger.kernel.org
cc: io-uring@vger.kernel.org
cc: x86@kernel.org
Link: https://lore.kernel.org/r/20210505110310.237537-1-metze@samba.org
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.